Adding solar panels

[Mike90250]

So, you must have several strings of PV wired to the charge controller. At your combiner box, shut all strings but one, down. let controller stabilize, and record the power, and then add another string, remove the first, let stabilize, and record the power until you have tested and recorded all strings. All should be within a couple % of the rest. You may have some bad panels, and comparing strings is the quick way to test for them.

I've got 800ah of batteries @ 48V, and 5kw of PV, and just able to get by in winter with 7kwh daily usage, 2 cloudy days, and I need generator. If you are over paneled, you can switch some strings off in the summer and bring them back on for cloudy conditions. Having a decent combiner box with breakers is critical.

[-robw-]

So, you must have several strings of PV wired to the charge controller. At your combiner box, shut all strings but one, down. let controller stabilize, and record the power, and then add another string, remove the first, let stabilize, and record the power until you have tested and recorded all strings. All should be within a couple % of the rest. You may have some bad panels, and comparing strings is the quick way to test for them.

I've got 800ah of batteries @ 48V, and 5kw of PV, and just able to get by in winter with 7kwh daily usage, 2 cloudy days, and I need generator. If you are over paneled, you can switch some strings off in the summer and bring them back on for cloudy conditions. Having a decent combiner box with breakers is critical.

Done. Not yet in peak sun which hits 2 hours from now, but reached a high of 650~ watt output from Epever 3210. That's acceptable given sun, 780w max, and that the thing cost $80. Then turned on strings connected to Classic 150, one by one. All 5 between 4-4.2 amps, also acceptable given 5.3a IMP, sun, and age. Total current hitting batteries is 64 amps, 48.5a from Classic and 16.8a from Epever.

All that is consistent with my thoughts that this issue has nothing to do with input, and everything to do with batteries internal resistance. Even now, as the Classic 150 was ramping up to its present 48a the Epever was dropping down to 17a. The batteries just won't accept more than 60~ amps.

I tested end of strings with my ammeter and results are 30.08a on 1st string, and 31.4a on 2nd string. So connectivity isn't issue. Only thing left, imo, is 3 month old batteries.

As I post this total current has increased to 64.8a

.

[-robw-]

I want to add that 60a isn't actually the issue. With clouds being outlawed here 300 amps is easy to accomplish with 60 amp current. The actual problem is how once absorb voltage is hit and current starts dropping, I'll find the SOC at around 75% and current dropped all the way below 20 amps. That's why I can't top SG.

[Mike90250]

That's the way a 3 stage charger works, max amps till Absorb voltage is reached, then the amps taper off thru the whole absorb. Usually Absorb is 3 or so hours , fancy controllers you can preset so that at 10% of max amps. it terminates Absorb and drops to FLoat, which can still continue to top off the batteries.

MS_charge_stages.png

[-robw-]

For sure, but when I have 2580 PV watts available, and the Classic's 5 hr absorb stage completes with ending amps at around 8 but SG is only 1.22 something ain't right.

[-robw-]

What is strange is that 1800watts should deliver over 60amps into a 24V battery system. Those 8 CR305 wired 2Px4S create a 610Ah 24V system which should match up to that Classic 150 just fine.

My first concern is having a second pv charging system connected to the same batteries.
My second concern is having 1080w connected to the Epever 3210 which exceeds it's max watt input by close to 300watts. Unless you point the panels in different directions you could overload the Epever.

"My first concern is having a second pv charging system connected to the same batteries"

So... on that idea. My understanding is that if you install mismatched panels the system voltage will degrade to lower VMP but IMP will still be added to array. If the Classic sizing tool indicates my 150 can handle the additional 4 panels I installed, and the VMP difference between the older (36.5 vdc) and newer panels (31.3 vdc) is acceptable wattage loss, can I try doing that to see if it improves things? VOC of old is 43.8. VOC of new is 38.5.

Thanks

[-robw-]

"My first concern is having a second pv charging system connected to the same batteries"

So... on that idea. My understanding is that if you install mismatched panels the system voltage will degrade to lower VMP but IMP will still be added to array. If the Classic sizing tool indicates my 150 can handle the additional 4 panels I installed, and the VMP difference between the older (36.5 vdc) and newer panels (31.3 vdc) is acceptable wattage loss, can I try doing that to see if it improves things? VOC of old is 43.8. VOC of new is 38.5.

Bingo!

That did it. On the whole I'm wasting some wattage from the older array but as far as resolving issues, that fixed it. Max output with Classic 150 and Epever 3210 = 64~ amps. Max amperage with Classic 150 handling both arrays was 74.4 today. SG end of day is 1.26.

Batteries handled it well with no more bubbling than usual. Only issue presented was how much hotter the Classic got, with FET and PCB both around 69C. But Midnite Solar told me that is way under unit tolerance. It won't perform as well but it won't melt either.

Even the 2 arrays weren't all that mismatched on vdc, probably because of age and possible dust buildup on 1st array. When I put my voltmeter to every series all voltages (on load to Classic) were between 65.7 and 68.1. So the new panels are just like the old panels except they contribute 3x the amps to system.

Thanks for all input, folks.

[SunEagle]

Bingo!

That did it. On the whole I'm wasting some wattage from the older array but as far as resolving issues, that fixed it. Max output with Classic 150 and Epever 3210 = 64~ amps. Max amperage with Classic 150 handling both arrays was 74.4 today. SG end of day is 1.26.

Batteries handled it well with no more bubbling than usual. Only issue presented was how much hotter the Classic got, with FET and PCB both around 69C. But Midnite Solar told me that is way under unit tolerance. It won't perform as well but it won't melt either.

Even the 2 arrays weren't all that mismatched on vdc, probably because of age and possible dust buildup on 1st array. When I put my voltmeter to every series all voltages (on load to Classic) were between 65.7 and 68.1. So the new panels are just like the old panels except they contribute 3x the amps to system.

Thanks for all input, folks.

I am glad your batteries are ok with your CC arrangement. Keep us informed on how it performs.

[OggYSD]

If you have a 1.5kW inverter, you can have up to 2kW of panels attached.

If you have a 3kW inverter you can have up to 4kW of panels attached.

If you have a 5kW inverter you can have up to 6.65kW of panels attached.

And if you don’t go over the 133%, you can claim the solar rebate (STCs) on those extra panels which will cover a big chunk of their of their cost (excluding installation costs and installer margin).

Moderator edit: Please, no more advertising links, thanks.

[bcroe]

If you have a 1.5kW inverter, you can have up to 2kW of panels attached.
If you have a 3kW inverter you can have up to 4kW of panels attached.
If you have a 5kW inverter you can have up to 6.65kW of panels attached.

My DC:AC ratio is over 2.3:1. That works because the panels are split between E and W,
giving the same peak power for more hours. And and a 2 sided array can mount twice as
many panels for about the same cost. Bruce Roe 3Direction.JPG

[Ampster]

...
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And if you don’t go over the 133%, you can claim the solar rebate (STCs) on those extra panels which will cover a big chunk of their of their cost (excluding installation costs and installer margin).

A few years ago I took the full Investment Tax Credit (ITC) on a system with a DC to AC ratio of 1.5 to one. I do not recall even having to state the DC to AC ratio on that or any of my previous ITC deductions. It was simply the total cost that was used. Is that stated somewhere in the IRS Regulations?
I am not familiar with the term STCs as it pertains to the ITC. In the solar world STC usually refers to Standard Test Conditions.